Dysfunctions related to age can be defined as the age-related loss of function of organs in people. Lot of dysfunctions can appear in the brain and be responsible in part of degenerative diseases but also in muscles. In this case, people with dysfunctions of their muscle suffer of sarcopenia.
Sarcopenia can be defined as the age-related loss of muscle mass, strength and function (Waters, Baumgartner & Garry 2000; Vandervoort & Symons 2001). Although there is no specific level of lean body mass or muscle mass at which one can say sarcopenia is present (Roubenoff 2001), any loss of muscle mass is of importance because there is a strong relationship between muscle mass and strength (Roth, Ferrell & Hurley 2000). Sarcopenia appears to begin in the fourth decade of life and accelerates after the age of approximately 75 years (Waters, Baumgartner & Garry 2000). With aging and inactivity, the most atrophy is seen in the fast twitch (FT) fibers which are recruited during high-intensity, anaerobic movements. Although sarcopenia is mostly seen in physically inactive individuals, it is also evident in individuals who remain physically active throughout their lives. This finding suggests that physical inactivity is not the only contributing factor to sarcopenia. Current research is finding that the development of sarcopenia is a multifactorial process. Many factors, including physical inactivity, motor-unit remodeling, decreased hormone levels, and decreased protein synthesis; may all contribute to sarcopenia.
Although sarcopenia may be partly reversible with appropriate exercise interventions, there is a need to find original treatment of sarcopenia.
Apelin is a peptide, identified as the endogenous ligand of APJ, an ubiquitously expressed G protein coupled receptor (Tatemoto K, Hosoya M, Habata Y, Fujii R, Kakegawa T, Zou M X, Kawamata Y, Fukusumi S, Hinuma S, Kitada C, Kurokawa T, Onda H, Fujino M. Isolation and characterization of a novel endogenous peptide ligand for the human APJ receptor. Biochem Biophys Res Commun. October 251(2):471-6. 1998). Apelin is synthesized as a 77-amino acid prepropeptide that is cleaved in different fragments including apelin-36, apelin-17, apelin-13 and the post-translationally [Pyr1] apelin-13 with a conversion of the N-terminal glutamate to pyroglutamate preventing enzymatic breakdown and thus preserving biological activity (Tatemoto K, Hosoya M, Habata Y, Fujii R, Kakegawa T, Zou M X, Kawamata Y, Fukusumi S, Hinuma S, Kitada C, Kurokawa T, Onda H, Fujino M. Isolation and characterization of a novel endogenous peptide ligand for the human APJ receptor. Biochem Biophys Res Commun. October 251(2):471-6. 1998). Before to be revealed as an adipocyte-secreted factor (Boucher et al, Endocrinology, 2005), apelin was known to exert several central and peripheral effects in different tissues such as the regulation of the cardiovascular, immune and gastrointestinal functions but also in fluid homeostasis, angiogenesis, proliferation of different cell types and embryonic development (see for example US2008/0182779, US2010/0221255 or US2005/0075275). However its role in dysfunctions associated with aging has not yet been identified.